Fixing a leaking toilet can sometimes be a bit of a challenge. Without looking at it, it is hard to know what is causing your leak, so giving you a straight answer on what to do is tough. The best advice I could give you is to call a professional plumber.
If you have no experience fixing toilets or doing any sort of plumbing, then there is a chance that you could make things worse by tinkering and trying to fix the leak. Usually, for things like a leak, a plumber can come out to you within the same day and get the issue sorted. I recently had the same issue and I called a plumber in worthing. They fixed it within a couple of hours of my call, and it saved me from having to wait at home and miss work. I would definitely recommend calling a plumber over attempting to fix it yourself.